The invention relates to improvements in methods of and in apparatus for the making of filter plugs or filter mouthpieces for cigarettes or other rod-shaped articles of the tobacco processing industry. More particularly, the invention relates to improvements in methods of and in apparatus for converting a continuous tow of originally crimped filamentary filter material for tobacco smoke (such as cellulose acetate fibers) into a rod-like filler which is ready to be draped into a web of cigarette paper or other suitable wrapping material to form a continuous filter rod ready to be subdivided into filter rod sections or filter mouthpieces (plugs) of unit length or multiple unit length. Filter mouthpieces of unit or multiple unit length can be fed into the magazine of a so-called tipping machine wherein the filter mouthpieces are connected (normally by so-called uniting bands of artificial cork or the like) with plain cigarettes of unit length of multiple unit length to form therewith filter cigarettes of unit length or multiple unit length.
In accordance with the presently prevailing practice, a filter tow is drawn from a bale and is thereupon subjected to a series of special treatments including spreading or banding and stretching of its filaments to thus convert the tow into a flat and relatively wide web or strip of parallel or nearly parallel filaments, and thereupon contacting the web with a suitable plasticizer (such as triacetin) to bond portions of neighboring filaments to each other. This ensures that the filaments in a finished filter mouth-piece define a maze of passages for the flow of tobacco smoke and the mouthpiece can intercept a high percentage of tar, condensate and certain other ingredients of tobacco smoke before the smoke reaches the smoker's mouth. The plasticizer applying station is followed by a so-called gathering or collecting station where the width of the web is reduced so that the thus treated tow resembles or again resembles a rod-like mass of filaments ready to be draped into cigarette paper or the like.
An important requirement for the making of satisfactory filter mouthpieces is to ensure that the homogeneousness of the filler in each of a short or long series of successively formed filter mouthpieces fluctuates very little or not at all, and that such homogeneousness matches or very closely approximates an optimum value. Furthermore, each unit length of the tow must yield a high number of fillers for filter mouthpieces. As a rule, the making of lightweight filter mouthpieces which, in spite of the relatively small quantity of filamentary filter material therein, constitute satisfactory barriers to the penetration of tar and condensate into a smoker's mouth renders it even more important and necessary to enhance the homogeneousness of successive increments of the treated tow which is ready to be converted into the filler of a filter rod. Another desirable characteristic of a satisfactory filter mouthpiece is a rather pronounced resistance to the flow of tobacco smoke therethrough.
U.S. Pat. No. 5,590,449 discloses an apparatus wherein so-called banding nozzles are utilized to separate the filaments in successive increments of the running tow ahead of the so-called stretching zone in which the conversion of the tow into a relatively wide and flat strip or web of parallel or substantially parallel filaments is completed. Such web is thereupon advanced through the plasticizing station and thereafter through the gathering station prior to admission into the filter rod forming zone. The introduction of successive increments of the gathered web into the rod forming station can be preceded by a treatment with a stream of compressed air and the passage through the so-called gathering horn.
Reference may also be had to U.S. Pat. No. 3,974,007 which discloses a method of and an apparatus for the formation of filter rod sections, and to U.S. Pat. No. 4,721,119 which discloses a rod making machine wherein a web of cigarette paper or the like can be draped around a rod-like filler of fibrous material of the tobacco processing industry.
It has been found that, in many instances, spreading, stretching and other presently known treatments of a tow of filamentary filter material for tobacco smoke cannot invariably and reliably ensure the elimination of all undesirable accumulations (such as clumps) of non-separated filaments ahead of the wrapping station. This results in the making of filter mouthpieces exhibiting an unacceptable resistance to the flow of tobacco smoke and/or other undesirable characteristics of the ultimate products.
Furthermore, the path for the advancement of filamentary filter material from the source of tow (such as the aforementioned bale) to the wrapping station is likely to contain filaments which became separated from the main body of the tow that is being advanced through the banding, stretching, plasticizing and gathering stations. The presence of loose filaments of cellulose acetate in the path which is provided for the advancement of the tow toward the wrapping station and/or in the atmosphere surrounding a production line including one or more filter rod making machines, one or more filter tipping machines and normally one or more additional (such as packing, cellophaning and other) machines is highly undesirable for a number of reasons.